This invention relates to variable pitch fans.
Flexxaire Manufacturing Inc. makes a variable pitch fan for use on engines, such as engines made by Caterpillar Inc. of Peoria, Ill., USA. A goal of variable pitch fan design is to provide a variable pitch fan which is lightweight, reliable, and which provides accurate and rapid adjustment of fan. There are various variable pitch fans known, as for example those described in U.S. Pat. Nos. 5,564,899; 5,022,821; and 5,122,034. It is an object of the invention to provide improved operating features for variable pitch fans.
There is thus provided, in accordance with an aspect of the invention, a variable pitch fan, which has a piston extending axially from a main shaft, about which main shaft a fan blade hub rotates. A pitch shifter is mounted on a cylinder, which itself is mounted on the piston. The pitch shifter is actuated by hydraulic fluid for example supplied through the main shaft to the cylinder. The piston is preferably axially stationary in relation to the main shaft. Relative rotational movement between the piston and cylinder is prevented by use of a stop, by using out of round surfaces, as for example a hexagonal surface on one of the piston and cylinder.
According to a further aspect of the invention, a portion of the main shaft forms the other of the piston shaft and cylinder. According to a further aspect of the invention, the main shaft has a bore defining the cylinder, and the out of round exterior surface on the piston shaft is received by an out of round surface in the main shaft. The housing may be mounted for rotational movement on the main shaft on bearings, and lubrication for the bearings may be delivered by a passageway through the piston shaft.
According to a further aspect of the invention, there is provided a pully hub mounted together with the housing for rotation on the main shaft.
In a further improvement of variable pitch fans, counterweights, which are known in themselves for use on aircraft propellers, are mounted on each fan blade of a variable pitch fan, preferably hydraulically actuated, in a position which generates a torque opposite in direction to torque generated by the fan blades. The counterweights may be overbalanced, underbalanced, or balanced.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.